The invention relates to a solid-state trip device for a multipole electrical circuit breaker with an operating mechanism of a separable contact system, comprising:
a measuring device having a current sensor per pole to detect the intensity of the current flowing in each active conductor of the alternating current system, and rectifying means, electrically connected with said sensor to deliver a first rectified control signal, proportional to the maximum intensity of the currents of the system.
a first electronic processing circuit of said first control signal, comprising at least one delayed or instantaneous trip circuit capable of sending with or without a time delay a tripping order to a solid-state switching device when said signal exceeds a predetermined threshold,
a trip coil electromagnet controlled by said switching device and acting on the mechanism, after the tripping order has been emitted, to open the separable contact system,
and a test circuit with auxiliary terminals which can be connected to a fault simulator designed to apply an artificial fault current to monitor operation of the solid-state trip device.
The use of a test circuit in an electronic circuit breaker is well-known in the art, and enables operation of the trip device to be tested by applying an artificial fault current which simulates an overload or short-circuit current. The intensity of this current is generally greater than the tripping threshold of the long or short time delay trip circuit. A first test possibility is carried out when the circuit breaker is disconnected from the mains, and the electronic trip device is supplied and the artificial fault current applied by connecting the fault simulator to the test terminals. Opening of the circuit breaker contacts, following a test, informs the operator that the electronic trip device is in proper working order.
A second test possibility is when the circuit breaker is in service connected to the mains to be monitored. U.S. Pat. No. 3,924,160 refers to a test circuit of a three-phase circuit breaker enabling a D.C. test current to be applied in parallel to a diode whose anode is connected to the positive output terminal of a rectifier bridge associated with one of the current transformers. The three rectifier bridges are connected in series and the electronic processing circuit is sensitive to the strongest current:
if the intensity of the phase current delivered by the current transformers is greater than the test current, the test circuit diode is forward biased, and the processing circuit receives the phase current only;
if the test current is greater than the phase current, the test circuit diode is reverse biased and the processing circuit responds to the test current only.
A test circuit of this kind enables the processing circuit to be adapted to the strongest current, the test then being independent from the phase current intensities. Operation of the trip device is not hindered by short-circuiting of the test terminals. The problem arising from this device is the polarization of the test terminals. It is in fact absolutely necessary that the diode anode be connected to the simulator negative pole, and the cathode to the simulator positive pole. An error in connecting the simulator causes the polarity to be reversed, leading to destruction of the diode and the electronic processing circuit.
U.S. Pat. No. 4,060,844 refers to a solid-state trip device for a three-phase circuit breaker comprising a measuring circuit with current transformers cooperating with two parallel rectifier bridges. A diode test circuit is connected in parallel on the D.C. side of the rectifier bridges, the test diode anode being connected to the simulator positive pole, and the cathode to the positive output terminal of the rectifier bridges. The negative output terminal of the bridges is connected to the simulator negative pole. A trip device of this kind is insensitive to short-circuiting of the test terminals, but the test still remains polarized giving rise to the above-mentioned drawbacks.
The object of the invention is to improve the reliability and safety of test circuits built into solid-state trip devices, independent from the mains configuration.